Landlords do not build they own. Contractors and developers build. If you could own one building and charge $2500 or own 5 building and charge $600 each, what would you choose? You would make $500 more owning more buildings, but you would also have more overhead and work managing them all.
The dominant factor driving house prices is mortgage credit inflation, not supply and demand, both the hypothesis and the data for this are very strong.
Sure, but in normal markets both supply and demand shift to reach equilibrium. In urban housing markets, increasingly supply is approximately illegal, so what would be manageable demand for any other resource drives runaway price growth like we see here.
The argument for not blaming high-salary tech workers is that when they demand anything other than housing (nootropics or standing desks or whatever other stereotype we might choose), prices don't react anywhere near as strongly.
Increasing supply shouldn't be that hard. High rise apartment buildings can house thousands of people using a small amount of real-estate. Opposition to them is mostly political. They do make it more difficult to design your city services, but that's not an insurmountable problem either.
The Bay area should look a lot more like Manhattan, not that Manhattan is the gold standard in affordable housing...